Generally, a broadband wireless access system defines a protocol of a medium access control (MAC) layer and a physical (PHY) layer for a point-to-multipoint connection between a base station and a mobile subscriber station. FIG. 1 is a diagram of protocol layer architecture of a broadband wireless access system.
A physical layer of a broadband wireless access system is mainly classified into a single carrier system and a multi-carrier system (OFDM/OFDMA). The multi-carrier system uses OFDM and employs OFDMA (orthogonal frequency division multiple access) as an access method that can allocate resources by sub-channel unit resulting from grouping carriers in part.
Forward error correction coding selectively uses concatenated code of RS code and convolutional code or block turbo code in common and employs BPSK/QPSK/16-QAM/64-QAM modulation. And, adaptive modulation/coding (AMC) is applied to select a modulation mode and coding rate system dynamically according to a channel status. For AMC, reception signal intensity, signal to noise ratio (CINR) or BER is used in measuring channel quality.
In an OFDMA physical layer, active carriers are separated into groups to be transmitted to different receiving sides per group. And, the group of carriers transmitted to one receiving side is called a sub-channel. Carriers constructing each sub-channel may be adjacent to each other or can be spaced apart to leave an equal distance from each other. Thus, although complexity is increased by enabling a multiple-access by sub-channel unit, it is advantageous in frequency diversity gain, gain according to power concentration and efficient execution of forward power control.
Slot allocated to each user is defined by a 2-dimensional data region and is a set of consecutive sub-channels allocated by a burst. In OFDMA, one data region is represented as a rectangle determined by a time coordinate and a sub-channel coordinate. This data region is allocated to an uplink of a specific user or a base station can transmit the data region to a specific user in downlink. To define the data region in a 2-dimensional space, a number of OFDM symbols in a time domain and a number of consecutive sub-channels starting from a place distant from a reference point by offset in a frequency domain should be given.
MAC data is segmented according to FFC (forward error correction) block size, and each FEC block is extended to occupy three OFDM symbols in a temporal axis of each sub-channel. Mapping keeps being performed by incrementing a sub-channel number for each FEC block until an end of data region is reached. If the end of data region is reached, mapping keeps being performed from an OFDM symbol having a next lower number in the same manner.
FIG. 2 is a diagram of an example of a process for mapping the FEC block to OFDMA sub-channel and OFDM symbol.
FIG. 3 is a diagram of a frame structure of an OFDMA physical layer in a broadband wireless access system. A downlink sub-frame starts from a preamble used for synchronization and equalization in a physical layer. Subsequently, a broadcast-formatted downlink map (DL-MAP) message and uplink map (UL-MAP) message, which define positions and usages of bursts allocated to downlink and uplink, respectively, follow the preamble to define an overall structure of a frame.
DL-MAP message defines a usage allocated per burst to a downlink interval in a burst mode physical layer, and UL-MAP message defines a usage of burst allocated to an uplink interval. Information elements configuring DL-MAP include DIUC (downlink interval usage code), CID (connection ID) and burst position information (sub-channel offset, symbol offset, No. of sub-channels, No. of symbols). And, a downlink traffic interval is identified on a user end by the information elements. Meanwhile, usages of information elements configuring UL-MAP message are decided per CID (connection ID) by UIUC (uplink interval usage code) and a position of a corresponding interval is determined by ‘duration’. In this case, a per-interval usage is determined according to a value of UIUC used by UL-MAP. And, each interval starts from a point distant from a previous IE start point by ‘duration’ regulated by UL-MAP IE.
DCD message and UCD message include modulation types, FEC code types and the like as physical layer associated parameters to be applied to burst intervals allocated to downlink and uplink, respectively. And, the DCD and UCD messages regulate parameters (e.g., values of R-S code, etc.) necessary for various forward error correction code types. Theses parameters are given by burst profiles regulated per UIUC and DIUC within UCD and DCD, respectively.
MAC layer of a broadband wireless access system is basically based on DOCSIS specifications as a cable modem standard of MCNS consortium. Core contents (MAC management system, resource allocation method & supported service, initialization procedure, etc.)) of MAC are similar to DOCSIS specifications except security guarantee according to radio system characteristics, support for various modulations and other partial addition sand revisions.
CS (service-specific convergence sublayer) is a layer existing above MAC CPS (common part sublayer) and performs a function of receiving PDU (protocol data unit) from an upper layer, a function of classification of upper layer PDU, a function of processing upper layer PDU based on this classification, a function of delivering CS PDU to appropriate MAC SAP and a function of receiving CS PDU from a peer entity. And, CS provides a function of classifying upper layer PDUs per connection and an optional function of compressing information of a payloader header or recovering the compressed header information.
MAC CPS maps each packet to a proper service follow in packet transmission between a mobile subscriber station and a base station based on a connection and offers QoS differing in level according to the connection-based service flow. A figure of MAC PDU defined in MAC CPS is explained as follows.
FIG. 4A is a diagram of a format of MAC PDU. MAC PDU is mainly classified into MAC management PDU and user data MAC PDU. The MAC management PDU uses a MAC management message previously regulated for MAC layer's activity as a payload and a MAC header is attached to each payload. And, a band request PDU necessary for each subscriber part to dynamically request a band required for uplink corresponds to a specially formatted MAC management PDU having a header called a request header only without a separate payload. Moreover, the band request header is made to be delivered via contention-based uplink band, thereby enabling a mobile subscriber station, which fails in having an uplink band allocated thereto by a base station, to request the uplink band. FIG. 4B is a diagram of an example of a band request header.
Packet PDU corresponding to user data is mapped to a payload of MAC SDU and becomes MAC PDU by having MAC header and CRC (optional) attached thereto. FIG. 4C is a diagram of an exemplary structure that a plurality of MAC PDUs concatenated with each other to be transmitted as one uplink burst. Each MAC PDU is identified by a generic connection ID (CID) and can be concatenated with a MAC management message, a band request PDU or the like as well as user data in the same burst.
MAC management message is constructed with a field indicating a type of a management message and a management message payload. DCD, UCD, UL-MAP, DL-MAP and the like among management messages correspond to representative management messages each of which directly regulates the aforesaid frame structure, band allocation and physical layer parameters.
A scheduling service is applied to improve efficiency in polling/transmission permission procedure. By clearly illustrating a scheduling service and QoS parameters associated with the scheduling service, a base station can estimate necessary extents of delay and throughput of uplink traffic and offers polling and transmission grant at a proper time correspondingly. Polling is a process that a base station allocates a bandwidth to each mobile subscriber station for a bandwidth request. Scheduling service types proposed by specifications are classified into UGS (Unsolicited Grant Service), rtPS (real-time Polling Service), nrtPS (non-real-time Polling Service) and BE (Best Effort). Additional band allocation request through piggybacking/polling is possible, and bandwidth stealing is possible for scheduling services of other types except UGS in a manner of redistributing a bandwidth allocated to one connection to another connection within an entire band allocated to each mobile subscriber station.
In transmitting downlink data burst to a mobile subscriber station from a base station in a broadband wireless access system, a downlink burst profile management of modifying coding and modulation schemes appropriately according to a downlink signal quality received by the mobile subscriber station is explained as follows.
A downlink burst profile is determined by a base station according to a quality of signal received by each mobile subscriber station. To reduce uplink traffic, a mobile subscriber station measures CINR (carrier to interference and noise ratio) and compares whether an average of CINR lies within an allowed operational range. This range is determined by a threshold level. If the received CINR deviates from the allowed operational range, the mobile subscriber station requests a new burst profile. If an uplink band is allocated to the mobile subscriber station by the base station, the mobile subscriber station transmits a DBPC-REQ (downlink burst profile change request) message using the allocated uplink band. The base station delivers DPBC-RSP (downlink burst profile change response) to the mobile subscriber station to make a response to the request made by the mobile subscriber station. Table 1 and Table 2 show examples of DBPC-REQ and DBPC-RSP messages, respectively.
TABLE 1SyntaxSizeNotesDBPC-REQ_Message_Format( ){Management Message8 bitsType = 23Reserved4 bitsShall be set to zeroDIUC4 bitsData grant DIUC values.Configuration Change8 bitsValue of Configuration ChangeCountCount provided in DCD definingthe burst profile associatedwith DIUC.}
TABLE 2SyntaxSizeNotesDBPC-RSP_Message_Format( ){Management Message8 bitsType = 24reserved4 bitsShall be set to zeroDIUC4 bitsData grant DIUC values.Configuration Change8 bitsValue of Configuration ChangeCountCount provided in DCD definingthe burst profile associatedwith DIUC.}
If a mobile subscriber station is not provided with an uplink band allocated by a base station and if the mobile subscriber station needs to make a request for a change of a downlink burst profile, the mobile subscriber station transmits such a ranging request (RNG-REQ) message as Table 3 in an initial ranging interval. Table 4 shows an example of TLV parameter included in a ranging request message such as Table 3.
TABLE 3SyntaxSizeNotesRNG-REQ_Message_Format( ) {Management Message Type = 48 bitsDownlink Channel ID8 bitsTLV Encoded InformationvariableTLV specific}
TABLE 4TypeName(1 byte)LengthValue (variable-length)Requested11Bits 0-3: DIUC of theDownlinkdownlink burst profileBurst Profilerequested by the SS fordownlink traffic.Bits 4-7: 4 LSB ofConfiguration Change Countvalue of DCD defining theburst profile associated with DIUC
The base station having received the ranging request (RNG-REQ) message transmits information about a downlink burst profile to be changed to the mobile subscriber station via such a ranging response (RNG-RSP) message as Table 5. And, Table 6 shows an example of TLV parameter included in the ranging response message.
TABLE 5SyntaxSizeNotesRNG-RSP_Message_Format( ) {Management Message Type = 58 bitsUplink Channel ID8 bitsTLV Encoded InformationvariableTLV specific}
TABLE 6TypeName(1 byte)LengthValue (variable-length)Downlink72This parameter is sent inOperationalresponse to the RNG-REQBurst ProfileRequested Downlink BurstProfile parameter.Byte 0: Specifies the leastrobust DIUC that may beused by the BS fortransmissions to the SS.Byte 1: ConfigurationChange Count value of DCDdefining the burst profileassociated with DIUC.
The mobile subscriber station selects a proper burst profile via such a threshold parameter included in DCD message as Table 7. FIG. 5 is a diagram for explaining a relation between CINR and a burst profile according to DIUC.
TABLE 7TypeName(1 byte)LengthValue (variable-length)FEC Code1501 0 = QPSK(CC) ½14 = QPSK(CTC) ¾type 1 = QPSK(CC) ¾15 = 16-QAM(CTC) ½ 2 = 16-QAM(CC) ½16 = 16-QAM(CTC) ¾ 3 = 16-QAM(CC) ¾17 = 64-QAM(CTC) ⅔ 4 = 64-QAM(CC) ⅔18 = 64-QAM(CTC) ¾ 5 = 64-QAM(CC) ¾19 = 64-QAM(CTC) ⅚ 6 = QPSK(BTC) ½20 = QPSK(ZTCC) ¾ 7 = QPSK(BTC) ¾ or ⅔21 = QPSK(ZTCC) ¾ 8 = 16-QAM(BTC) ⅗22 = 16-QAM(ZTCC) ½ 9 = 16-QAM(BTC) ⅘23 = 16-QAM(ZTCC) ¾10 = 64-QAM(BTC) ⅔ or ⅝24 = 64-QAM(ZTCC) ⅔11 = 64-QAM(BTC) ⅚ or ⅘25 = 64-QAM(ZTCC) ¾12 = QPSK(CTC) ½26 . . . 255 = reserved13 = QPSK(CTC) ⅔DIUC15110-3.75 dBMandatoryCINR at or below where this DIUCexitcan no longer be used and wherethresholdthis change to a more robust DIUCis required, in 0.25 dB units.DIUC15210-63.75 dBMinimumThe minimum CINR required toentrystart using this DIUC whenthresholdchanging from a more robust DIUCis required, in0.25 dB units.
In a broadband wireless access system, an idle mode is supported to reduce power consumption of a mobile subscriber station. In the idle mode, without performing handover in moving between base stations within a paging zone including a plurality of base station areas while not registered to a specific base station, a mobile subscriber station is made to periodically check a presence or non-presence of downlink traffic toward the mobile subscriber station itself by receiving a paging (MOB_PAG-ADV) message, whereby power consumption of the mobile subscriber station can be minimized.
To construct one paging zone, an inter-base station message (Paging-group-action), which has a format such as Table 9, transmitted between base stations by wire is used.
TABLE 9SizeField(bits)NotesPaging-group-actionMessage_Format( ) {Message Type8Sender BS-ID48Base station uniqueidentifier (same number asthat broadcasted on the DL-MAP message)Target BS-ID48Base station uniqueidentifier (same number asthat broadcasted on the DL-MAP message)Time Stamp32Number of milliseconds sincemidnight GMT (set to0xffffffff to ignore)Action40 - Assign target BS topaging groups1 - Remove target BS frompaging groups2 - Query (which paginggroups target BS belongsto ?)3 - Information (paginggroup sender BS belongs to)Num Records4Number of paging-group-IDrecordsFor (j=0; j<NumRecords; j++) {Paging-group-ID16Paging-group-IDPAGING_CYCLE16Cycle in which the pagingmessage is transmittedwithin the paging groupPAGING OFFSET3MSS PAGING OFFSET parameter}Security fieldTBDA means to authenticate thismessageCRC field32IEEE CRC-32}
The paging-group-action message is delivered between a paging controller station and a base station or between base stations. The paging-group-action message can be used for the following four kinds of usages according to combinations of action bits.
First of all, a receiving base station (target BS) can be designated as a specific paging group (Action=0). Secondly, a receiving base station can be excluded from a specific paging group (Action=1). Thirdly, it can be queried that a receiving base station belongs to which paging group (Action=2). Fourthly, it can be indicated that a transmitting base station (sender BS) belongs to which paging group (Action=3).
Since a specific base station can belong to at least one paging zone, the paging-group-action message can include information about a plurality of paging groups. Base stations can know a paging cycle and a paging offset used by each paging zone via the paging-group-action message. It is possible to dynamically assign base station to a paging group via the paging-group-action message.
FIG. 6 is a diagram of an example that a plurality of base stations supporting idle mode belong to a paging group to construct a paging zone.
To enter an idle mode, a mobile subscriber station uses a deregistration request (DREG_REQ) message shown in Table 10.
TABLE 10SyntaxSizeNotesDREG-REQ_message_format( ){Management Message Type =8 bits49De-8 bits0x00 = MSS de-registration_Request_Coderegistration requestfrom BS and network0x01 = request for MSSde-registration fromServing BS andinitiation of MSS IdleMode0x02-0xFF = ReservedTLV encoded parametersvariable}
Table 11 explains details of ‘TLV encoded parameters’ of the deregistration request message.
TABLE 11NameTypeLengthValuePaging2Requested cycle in which theCyclepaging message is transmittedRequestwithin the paging group.Idle Mode1MSS request for Paging ControllerRetainretention of network re-entryInformationrelated MAC management messageMSS service and operationalinformation to expedite futureNetwork Re-entry from Idle Mode.For each Bit location, a value of‘0’ indicates the informationassociated with the specified MACmanagement message is notrequested to be retained andmanaged, a value of ‘1’ indicatesthe information is requested tobe retained and managed.Bit #0: Retain MSS service andoperation information associatedwith SBC-REQ/RSP MAC managementmessagesBit #1: Retain MSS service andoperational informationassociated with PKM-REQ/RSP MACmanagement messagesBit #2: Retain MSS service andoperational informationassociated with REG-REQ/RSP MACmanagementBit #3: Retain MSS service andoperational informationassociated with Network AddressBit #4: Retain MSS service andoperational informationassociated with Time of DayAcquisitionBit #5: Retain MSS service andoperational informationassociated with TFTP MACmanagement messagesBit #6: Retain MSS service andoperational informationassociated with Full service (MACstate machines, CS classifierinformation, etc.)
A mobile subscriber station can make request to enter an idle mode by setting a De-registration Request Code of the deregistration request message to 0x01 and by delivering it to a base station. (In this case, management resource information, which a base station intends to retain, of a mobile subscriber station can be delivered to the base station after a preferred paging cycle and entry to idle mode.)
The base station having received the deregistration request message from the mobile subscriber station can make a response to an idle mode entry request of the mobile subscriber station via a deregistration command (DREG_CMD) message shown in Table 12.
TABLE 12SyntaxSizeNotesDREG-CMD Message Format( ) {Management Message Type = 298 bitsAction Code8 bitsTLV encoded parametersvariable}
The base station allows an idle mode entry via Action Code of a deregistration command (DREG_CMD) message (Action Code=0x05), makes an idle mode entry requested again after a predetermined duration (Action Code=0x06), or can make an idle mode entry not requested no more until it transmits the deregistration command message (Action Code=0x07).
Action codes and their meanings of the deregistration command message are explained in detail in Table 13.
TABLE 13ActionCodeAction0x00MSS shall immediately terminate service with theBS and attempt network entry at another BS0x01MSS shall listen to the current BS but shall nottransmit until an RES-CMD message or DREG_CMD withAction Code 0x00 is received.0x02MSS shall listen to the current BS but onlytransmit on the Basic, Primary Management, andSecondary Management Connections.0x03MSS shall return to normal operation and maytransmit on any of its active connections.0x04MSS shall terminate current Normal Operations withthe BS; the BS shall transmit this action codeonly in response to any MSS DREG-REQ0x05require MSS de-registration from Serving BS andrequest initiation of MSS Idle Mode0x06The MSS may retransmit the DREG-REQ message afterthe time duration (REQ-duration) provided in themessage0x07The MSS shall not retransmit the DREG-REQ messageand shall wait the DREG-CMD message0x08-0xFFReserved
Through TLV (Type Length Value) item that can be selectively included in the deregistration command message, Paging Group ID, Paging_Cycle and Paging_Offset values, which should be retained by a corresponding mobile subscriber station during an idle mode, can be delivered. Table 14 illustrates paging information included as TLV parameter in a deregistration command message, mobile subscriber station's management resource information retained by a base station after completion of mobile subscriber station's idle mode entry, a paging controller identifier and the like. Informations, which a retained by a base station when a mobile subscriber station enters an idle mode, are provided to enable fast network registration and location update of the mobile subscriber station in a manner that a procedure for acquiring corresponding information in a network registration process can be omitted if a corresponding mobile subscriber station terminates idle mode or executes a location update procedure in the future.
TABLE 14NameTypeLengthValuePaging4Bits 15:0 - PAGING_CYCLE - CycleInformationin which the paging message istransmitted within the paginggroupBits 23:16 - PAGING OFFSET - Determines the frame within thecycle in which the pagingmessage is transmitted. Must besmaller than PAGING CYCLE valueBits 31:24 - Paging-group-ID - ID of the paging group the MSSis assigned toREQ-duration1Waiting value for the DREG-REQmessage retransmission (measuredin frames)Paging6This is a logical networkControlleridentifier for the Serving BS orIDother network entity retainingMSS service and operationalinformation and/or administeringpaging activity for the MSSwhile in IDLE modeIdle Mode1Idle Mode Retain Information isRetainprovided as part of this messageInformationis indicative only. Network Re-entry from Idle Mode processrequirements may change at timeof actual reentry. For each bitlocation, a value of ‘0’indicates the information forthe associated reentrymanagement messages shall not beretained and managed, a value of‘1’ indicates the informationfor the associated reentrymanagement message shall beretained and managed.Bit #0: Retain MSS service andoperational informationassociated with SBC-REQ/RSP MACmanagement messagesBit #1: Retain MSS service andoperational informationassociated with PKM-REQ/RSP MACmanagement messagesBit #2: Retain MSS service andoperational informationassociated with REG-REQ/RSP MACmanagement messagesBit #3: Retain MSS service andoperational informationassociated with Network AddressBit #4: Retain MSS service andoperational informationassociated with Time of DayBit #5: Retain MSS service andoperational informationassociated with TFTP MACmanagement messagesBit #6: Retain MSS service andoperational informationassociated with Full service(MAC state machines, CSclassifier information, etc.)
Thereafter, the mobile subscriber station can retain or terminate the idle more by receiving a paging broadcast (MOB-PAG-ADV) message shown in Table 15 at a determined paging cycle and paging offset.
TABLE 15SyntaxSizeNotesMOB_PAG-ADV_Message_Format( ) {Management Message8 bitstype=62Num_Paging_Group_IDs8 bitsNumber of paging groupIDs in this messageFor (i=0;i<Num_Paging_Group_IDs;i++) {Paging Group ID8 bits}Num_MACs8 bitsNumber of MSS MACaddressFor (j=0; j<Num_MACs;j++) {MSS MAC Address hash24 bits The hash is obtained bycomputing a CRC24 onthe MSS 48-bit MACaddress. The polynomialfor the calculation is0x864CFB.Action Code2 bitsPaging actioninstruction to MSS00 = No Action Required01 = Perform Ranging toestablish location andacknowledge message10 = Enter Network11 = reservedReserved6 bits}TLV Encoded InformationvariableTLV specificreservedvariablePadding bits to ensureoctet aligned}
Configuration of Multicast Broadcast Service (hereinafter abbreviated MBS) in a broadband wireless access system is explained as follows.
First of all, Multicast Broadcast Service (hereinafter abbreviated MBS) is a point-to-multipoint service that data is transmitted to a plurality of receivers from one source, by which the same data is transmitted to a plurality of receivers via a common radio channel for an efficient use of radio resources.
FIG. 7 and FIG. 8 are diagrams of examples of a reference model for MBS of a broadband wireless access system.
Referring to FIG. 7, configurational elements for MBS include an MBS contents server (Media Server), an MBS distribution server, base stations (BS) and mobile subscriber stations (MSS). The MBS contents server offers MBS data to the base stations and performs authentication of the mobile subscriber station and encryption key distribution for MBS contents. The MBS distribution server takes charge of scheduling of the MBS data to be delivered to a plurality of the base station. Optionally, the MBS distribution server can be omitted so that the MBS contents server play a scheduling role of the MBS data. The base station provides the MBS data received via a backbone network to the mobile subscriber station via radio interface, and the mobile subscriber station receives the MBS data from the base station.
MBS in a broadband wireless access system can be classified into single base station MBS and multiple base station MBS. The single base station MBS need not use MBS associated parameters identically to deliver the MBS data between base stations but enables point-to-multipoint data transmission by assigning the same MBS associated parameter to mobile subscriber stations attempting to receive specific MBS data within a base station.
The multiple base station MBS delivers MBS data to mobile subscriber stations in a manner of using same MBS associated parameter for a specific MBS between base stations constructed with MBS zone. To enable a mobile subscriber station to recognize MBS zone, MBS zone ID is delivered to a mobile subscriber station. The mobile subscriber station can immediately check whether a currently retained MBS parameter is valid via the MBS zone ID received from the base station. In case that the mobile subscriber station moves away into another base station within the same MBS zone, it is unnecessary to perform a procedure for re-establishing MBS associated parameter to receive MBS data. And, by transmitting MBS data using the same radio resource at the same time, base stations within the same MBS zone can raise MBS data reception efficiency of mobile subscriber stations by macro diversity effect.
MBS of a broadband wireless access system has the following characteristics.
1) Power Consumption Minimization: Mobile subscriber station can minimize power consumption regardless of a current operational mode (e.g., normal operational mode, sleep mode, idle mode) while receiving MBS data.
2) Mobility: Mobile subscriber station is provided with seamless MBS connection while moving between base stations.
3) MBS Zone: MBS contents are transmitted via regionally classified MBS zone and MBS setting information (e.g., MBS connection identifier, encryption key, service identifier, etc.) can be configured different between different MBS zones.
4) Security: MBS contents are delivered to authenticated users only. An encryption key for MAC PDU of MBS data is equally applicable between base stations within MBS zone.
FIG. 9A and FIG. 9B explain an MBS operation of a broadband wireless access system.
(1) Mobile subscriber station attempting to search MBS contents in idle mode terminates an idle mode and then enters a normal operational mode.
(2) The mobile subscriber station makes a request for an MBS list to at lest one MBS contents server via HTTP request message.
(3) The MBS contents server transmits an HTTP response message containing the MBS list to the corresponding mobile subscriber station. The MBS list contained in the HTTP response message may include such information as an MBS contents name, a multicast IP address, a pot number and the like.
(4) The mobile subscriber station having acquired MBS information enters an idle mode or sustains a normal operational mode.
(5) After having acquired the MBS information, the mobile subscriber station delivers a service generation request (DSA-REQ) message containing multicast IP address and port number of specific MBS contents. (Service request message can be delivered to the mobile subscriber station by a base station).
(6) A base station delivers DSx-RVD message indicating a service request message reception to the mobile subscriber station and carries out an authentication procedure for deciding whether a user is suitable for MBS contents reception of the corresponding mobile subscriber station.
(7) Having carried out the authentication procedure, the base station includes downlink parameter information (e.g., service identifier, multicast connection identifier, QoS parameter, security association identifier (SAID), etc.) in a service generation response (DSA-RSP) message and then delivers the message to the corresponding mobile subscriber station.
(8) The mobile subscriber station delivers a key request message (PKM-REQ) to the base station to acquire an MBS key for decoding encrypted MBS PDU from the base station.
(9) The base station delivers a key response message (PKM-RSP) containing the MBS key to the corresponding mobile subscriber station.
(10) The mobile subscriber station receives encrypted MAC PDU for the corresponding MBS contents and then decodes the received MAC PDU via a key received from the base station.
An MBS zone is explained as follows.
MBS associated parameters (e.g., security key, multicast connection identifier, etc.) can be set different according to a region, and MBS contents can be broadcast within a limited zone. So, in moving away into another base station or performing handover, a mobile subscriber station receiving MBS contents needs to decide whether stored MBS information is valid and whether MBS contents can be continuously received. If a current base station provides MBS via parameter different from the MBS information retained by the mobile subscriber station or does not transmit the MBS contents at all, the mobile subscriber station should access a new base station to update the parameter for the MBS contents. To solve this problem, an MBS zone grouping at least one or more MBS providing base stations is managed in a broadband wireless access system.
Base stations within a same MBS zone transmit MBS contents to mobile subscriber stations using the same MBS parameter. And, MBS zone ID is delivered to a mobile subscriber station to enable the mobile subscriber station to recognize MBS zone. The mobile subscriber station can immediately confirm whether a currently retained MBS parameter is valid via the MBS zone ID received from the base station. In case of moving away into another base station within the same MBS zone, the mobile subscriber station does not need to perform a procedure for resetting the MBS associated parameters to receive MBS data. Moreover, by transmitting MBS data at the same time using the same radio resource, base stations within the same MBS zone can raise MBS data reception efficiency of mobile subscriber stations through macro diversity effect.
An operation for power consumption minimization of a mobile subscriber station receiving MBS data is explained as follows.
First of all, a mobile subscriber station can reduce power loss for a period of receiving MBS data regardless of a current operational mode (e.g., normal operational mode, sleep mode, idle mode). A downlink map information element (DL-MAP IE) contained in a downlink map (DL-MAP) message is defined to indicate a burst that is transmitted in a current frame. Yet, a mobile subscriber station should receive and decrypt a downlink map message each frame to receive a broadcast-formatted burst. In this case, it is unable to reduce power consumption. Yet, MBS map information element (MBS_MAP IE) enables a mobile subscriber station not to interpret a downlink frame including a downlink map message for a frame having MBS data not delivered thereto in a manner of informing the mobile subscriber station how many frames will take for MBS data burst to be delivered. So, the MBS map information element (MBS_MAP IE) enables the mobile subscriber station to minimize its power consumption. In particular, MBS_MAP IE has a considerable power saving effect on a mobile subscriber station in sleep or idle mode. Scheduling information of the MBS data burst can be delivered via MBS_MAP IE as one of DL-MAP IE or can be delivered in such a MAC management message format as an MBS MAP message. Table 16 and Table 17 show examples of MBS_MAP IE and MBS MAP message, respectively.
TABLE 16SizeSyntax(bits)NotesMBS_MAP_IEExtended DIUC4MBS_MAP = 0x05Length4Multicast CID1212 LSB of CID for multicastMBS Zone7MBS Zone identifier correspondsidentifierto the identifier provided by theBS at connection initiationMacro10 = Non Macro-Diversity enhanceddiversityzoneenhanced1 = Macro-Diversity enhanced zoneIf(Macrodiversityenhanced = 1){Permutation20b00 = PUSC permutation,0b01 = FUSC permutation,0b10 = Optional FUSC permutation,0b11 = Adjacent subcarrierpermutationIdcell6OFDMA Symbol8OFDMA symbol offset with respectOffsetto start of the MBS portionBoosting3It is used to indicate whetherboosting is used or not forMBS_MAP message.000: normal (not boosted)001: +6 dB010: −6 dB011: +9 dB100: +3 dB101: −3 dB110: −9 dB111: −12 dBDIUC4DIUC for MBS_MAP message in MBSportionNO.6It is indicated the size ofSubchannelsMBS_MAP message in MBS portion.NO. OFDMA2It is indicated the size ofsymbolsMBS_MAP message in MBS portion.}else{DIUC4OFDMA Symbol8The offset of the OFDMA symbol inOffsetwhich the burst starts, measuredin OFDMA symbols from beginningof the downlink frame in whichthe DL-MAP is transmitted.Subchannel6The lowest index OFDMA subchanneloffsetused for carrying the burst,starting from subchannel 0.Boosting3000: normal (not boosted)001: +6 dB010: −6 dB011: +9 dB100: +3 dB101: −3 dB110: −9 dB111: −12 dBNO. Symbols7NO.6SubchannelsRepetition20b00 - No repetition codingCoding0b01 - Repetition coding of 2Indicationused0b10 - Repetition coding of 4used0b11 - Repetition coding of 6usedNext MBS Frame8The Next MBS frame offset valueoffsetis lower 8 bits of the framenumber in which the BS shalltransmit the next MBS frame.Next MBS OFDMA8The offset of the OFDMA symbol inSymbol offsetwhich the next MBS portionstarts, measured in OFDMA symbolsfrom the beginning of thedownlink frame in which the MBS-MAP is transmitted.}If!(byteboundary){Padding NibblevariablePadding to reach byte boundary }}
TABLE 17SizeSyntax(bits)NotesMBS-MAP Message Format( ){Management Message Type = ?4Frame number4The frame number isidentical to the framenumber in the DL-MAPMBS_DIUC_Change_Count8#MBS_DATA_IE4Number of includedMBS_DATA_IEFor(i=0; i<n; i++){12 N = #MBS_DATA_IEMBS_DATA_IEvariable}8#MBS_DATA_Time_Diversity_IE4Number of includedMBS_DATA_Time_Diversity_IEFor(i=0; i<m; i++){M = #MBS_DATA_Timediversity IEMBS_DATA_Time_Diversity_IEvariable}TLV encoding elementIf(!byte boundary){Padding_Nibble}8
Table 18 shows an example of MBS_DATA_IE included in MBS MAP message.
TABLE 18SizeSyntax(bits)NotesMBS_DATA_IE{MBS_MAP type =40Multicast CID1212 LSB of CID for multicastMBS_DIUC4OFDMA Symbol8OFDMA symbol offset with respect toOffsetstart of the MBS portionSubchannel6offsetBoosting3000: normal (not boosted)001: +6 dB010: −6 dB011: +9 dB100: +3 dB101: −3 dB110: −9 dB111: −12 dBNO. OFDMA7symbolsNO.6SubchannelsRepetition20b00 - No repetition codingCoding0b01 - Repetition coding of 2 usedIndication0b10 - Repetition coding of 4 used0b11 - Repetition coding of 6 usedNext MBS frame8The Next MBS frame offset value isoffsetlower 8 bits of the frame number inwhich the BS shall transmit thenext BS frame.Next MBS OFDMA8The offset of the OFDMA symbol inSymbol offsetwhich the next MBS portion starts,measured in OFDMA symbols from thebeginning of the downlink frame inwhich the MBS-MAP is transmitted.}{
In the related art, MBS feedback information transmission of a mobile subscriber station for a change of MBS burst profile is defined as follows. A base station assigns an uplink band enabling a mobile subscriber station to transmit MBS feedback information via such a feedback polling IE as Table 19, and the mobile subscriber station transmits the MBS feedback information via such a feedback header as shown in FIG. 10 using the uplink band assigned by the base station.
TABLE 19SizeSyntax(bits)NotesFeedbackpolling IE( ){Extended UIUC4 bits0x??Length4 bitsLength in bytes of followingfieldsfor (i=0;i<NumberAllocations;i++){Feedback type6 bitsSee Table 7bIf(FeedbackMBS preferred DIUC feedbacktype ==0b10001){MBS CID16 bits Connect ID of the MBS connectionthat the MSS should feedback for}Else{Basic CID16 bits }UIUC4 bitsFeedback Type6 bitsSee Table 7bDuration10 bits In OFDMA slots (see 8.4.3.1)Allocation3 bitsThe UL feedback shall beOffsettransmitted in the frame which is0-8 frame delay relative to thecurrent framePeriod (p)2 bitsThe UL resource region isdedicated to the MS in every 2frame.Allocation3 bitsThe allocation is valid for 10 ×Duration (d)2d frame staring from the framedefined by Allocation_offset. Ifd == 0b000, the dedicatedallocation is de-allocated. If d ==0b111, the dedicated resourceshall be valid until the BScommands to de-allocate thededicated allocation.}Padding bitsVariableTo align octet boundary}
Having acquired uplink transmission synchronization with a base station via ranging procedure, a mobile subscriber station, of which management connection with a base station is released, in idle mode transmits MBS feedback information with an MBS feedback header, as shown in FIG. 10, to the base station using a contention-based uplink band (allocated via Feedback Polling IE or allocated for BW REQ header transmission) or can deliver an RNG-REQ message in which feedback information (Preferred DIUC, CCC, MBS CID) TLV parameter like Table 20 is included.
TABLE 20NameTypeLengthValueMBS FeedbackTBD3 bytePreferred DIUC for MBSInformationconnection identified by MBSCIDBits 3:0 - Preferred DIUC -Preferred DIUC for MBSconnectionBits 7:4 - CCC -Configuration Change Count ofDCD associated to DIUCBits 23:8 - MBS CID
In the related art, a base station changes a downlink burst profile (coding and modulation scheme) appropriately according to a downlink signal quality of a mobile subscriber station. So, the mobile subscriber station's reception error for downlink data transmitted from the base station by unicast can be minimized and the base station's radio resources can be efficiently used. Yet, in case of MBS data, since the MBS data is not the data a base station transmits to a specific mobile subscriber station by unicast but is transmitted in a broadcast format to corresponding mobile subscriber stations within a base station, it is difficult to provide proper burst profile to all mobile subscriber stations receiving the MBS data. And, it is also difficult to always transmit MBS data burst as robust burst profile for efficient use of resources. So, it is possible that MBS data cannot be received according to a channel status of each mobile subscriber station. In this case, it is possible to guarantee MBS data reception of mobile subscriber station by transmitting MBS data via burst profile suitable for the corresponding mobile subscriber station to receive.
In the related art, an uplink band allocated for MBS feedback transmission is allocated to a specific MBS connection on contention base between mobile subscriber stations. And, each mobile subscriber station receiving a corresponding MBS can transmit a feedback header using the same uplink band allocated through Feedback Polling IE. So, a base station receiving it may be unable to receive feedback information of a mobile subscriber station due to collisions in case that several mobile subscriber stations transmit feedback headers simultaneously. This may be a problem in selecting MBS burst profile as a value suitable for all mobile subscriber stations. Moreover, a mobile subscriber station is defined to transmit MBS feedback information to a base station using MBS feedback information only if unable to receive MBS data currently transmitted from a base station due to a degraded channel status. So, it may cause a problem that the base station always has to transmit MBS data via the most robust profile.
In the related art, in case of multiple base station MBS supporting macro-diversity, base stations within MBS zone should transmit the same MBS data to raise mobile subscriber station's MBS data reception efficiency on a boundary between base stations using the same channel resource, the same time domain and the same burst profile. This brings about difficulty in changing MBS data burst according to a channel status of each mobile subscriber station receiving MBS data. And, since MBS data is transmitted using a fixed burst profile, efficient use of base station resources is not facilitated. Besides, in order to provide MBS to an idle-mode mobile subscriber station capable of receiving MBS data with minimal power consumption without performing a handover procedure in moving between base stations while a management connection with a base station is released, the base station should transmit MBS data for MBS regardless of a presence or non-presence of the mobile subscriber station receiving the MBS data within the base station.